Drug delivery devices for setting and dispensing a single or multiple doses of a liquid medicament are as such well-known in the art. Generally, such devices have substantially a similar purpose as that of an ordinary syringe.
Drug delivery devices, in particular pen-type injectors have to meet a number of user-specific requirements. For instance, with patient's suffering chronic diseases, such like diabetes, the patient may be physically infirm and may also have impaired vision. Suitable drug delivery devices especially intended for home medication therefore need to be robust in construction and should be easy to use. Furthermore, manipulation and general handling of the device and its components should be intelligible and easy understandable. Moreover, a dose setting as well as a dose dispensing procedure must be easy to operate and has to be unambiguous.
Typically, such devices comprise a housing or a particular cartridge holder, adapted to receive a cartridge at least partially filled with the medicament to be dispensed. The device further comprises a drive mechanism, usually having a displaceable piston rod which is adapted to operably engage with a piston of the cartridge. By means of the drive mechanism and its piston rod, the piston of the cartridge is displaceable in a distal or dispensing direction and may therefore expel a predefined amount of the medicament via a piercing assembly, which is to be releasably coupled with a distal end section of the housing of the drug delivery device.
The medicament to be dispensed by the drug delivery device is provided and contained in a multi-dose cartridge. Such cartridges typically comprise a vitreous barrel sealed in distal direction by means of a pierceable seal and being further sealed in proximal direction by the piston. With reusable drug delivery devices an empty cartridge is replaceable by a new one. In contrast to that, drug delivery devices of disposable type are to be entirely discarded when the medicament in the cartridge has been completely dispensed or used-up.
With such multi-dose drug delivery devices at least a last dose limiting mechanism is required to inhibit setting of a dose exceeding the amount of medicament left in the cartridge. This is to avoid a potentially dangerous situation for the user believing that a set dose is entirely injected.
There already exist some drug delivery devices with end-of-content mechanisms or last dose mechanisms.
Document WO 2004/007003 A1 for instance discloses an end-of-content arrangement for preventing a dose setting member of an injection device to be set to a dose larger than the medicament remaining in the injection device. There is described a dose setting and injecting mechanism featuring an arm flexibly hinged to a coupling ring. Said arm is equipped with a cam engaging a spiral-shaped track provided on a driver. When a dose setting member and the coupling ring is rotated in a clockwise direction during the setting of a dose, the cam on the arm is moved along the track in an outward direction whereas the cam, during injection, due to the concomitant rotation of the coupling ring and the driver remains in its position in the track obtained during the dose setting.
The length of the spiral track is synchronised with the content in the cartridge such that the cam is guided out through the track opening when the cartridge is almost empty.
With many of these known approaches the last dose limiting mechanism is located rather remote from an actuation member, such like a dose dial member, by way of which the user may interact with the drive mechanism, e.g. for setting and/or dispensing of a dose. For limiting or delimiting a dose setting procedure, the angular momentum or driving force exerted by a user of the device has to be transferred from the actuation member almost through the entire drive mechanism and the plurality of its mutually interacting components until the last dose limiting mechanism is eventually activated and blocks a further dose incrementing movement of the drive mechanism and of its various components.
Since the mechanically interacting components of a drive mechanism are always subject to inevitable mechanical tolerances, a respective tolerance chain extending between the actuation member, e.g. a dose dial, and the last dose limiting mechanism may be fairly long. In effect, once a last dose limiting mechanism is activated and actually inhibits a dose incrementing displacement of e.g. a drive sleeve relative to a housing or relative to a piston rod, the locking or blocking of e.g. the drive sleeve has to propagate and to be transferred or returned to the dose dial member. Also here, due to the tolerance chain at least a minimal displacement, e.g. a rotation of the dose dial member may still be possible even though a dose incrementing displacement of the drive mechanism is effectively blocked.
It is therefore an object of the present invention to avoid disadvantages of known drug delivery devices and to provide a drive mechanism for a drug delivery device allowing for an intuitive operation, both for setting and for dispensing of a dose.
It is another object of the present invention to provide a drive mechanism for a drug delivery device for setting and dispensing of a dose of a medicament typically provided in a cartridge, wherein the drive mechanism is equipped with a last dose limiting mechanism. The last dose limiting mechanism should be rather precise and robust and should be easy to implement in the drive mechanism. The last dose limiting mechanism should further provide an immediate and an almost backlash-free feedback to the user when setting of a dose exceeding the amount of medicament left in the cartridge.
It is a further object to provide a drug delivery device featuring an improved last dose limiting mechanism.